This invention relates to an original reader such us an image scanner that reads image information on a manuscript, and especially relates to an original reader that provides a system for changing the optical resolution thereof.
A prior art flatbed type of original reader is shown in FIG. 17. In FIG. 17, a transparent manuscript platform 1, a manuscript 2, a reading unit 3 movable in the direction shown by the arrow (sub-scan direction), an optical source 4, lenses 6, and CCD (solid-state image sensor) substrate 7 are shown.
A surface of the manuscript 2 placed on the manuscript platform 1 is lighted by the optical source 4 of the reading unit 3. The reflected light from the manuscript surface 2 follows a rectangular path through the mirror 5, passes through the lens 6, and reaches CCD substrate 7 to be transformed into an electrical signal. The reading resolution of the manuscript 2 depends on the focal length of lens 6. The longer the focus is, the greater the magnification and the higher the resolution, but by these technique, the image angle becomes smaller, so the main scan size becomes also smaller.
Many of the prior art original reader include a mono focus lens system in which only one lens is used, and a lens exchangeable system in which two lenses of different focus distance are used.
Additionally, in a copy machine, there is a zoom lens system that may change magnification or resolution continuously by using a zoom lens.
FIGS. 18(a),(b),and (c) show diagrams of original reader of the prior art. FIG. 18(a) shows a mono focus lens system in which an image angle is fixed by xcex1 and a main scanning range of the original reader is fixed.
FIG. 18(b) shows an example of a lens switchover system in which either a field angle of xcex11 of which a lens of focus length is 75 mm, or field angle of xcex12 of which a lens focus length is 115 mm, is able to be chosen. The resolution of 800 dpi is obtained by an angle of view of xcex11, and the resolution of 2400 dpi is obtained by an angle of view of xcex12.
FIG. 18(c) shows a zoom lens system, and that resolution is changeable continuously from 800 dpi to 2400 dpi by changing zoom ratio.
The prior art original reader of mono focus lens is impossible to change resolution optically, and when resolution changing is necessary, there is no means other than an interpolating process for obtaining high resolution, and there are problems in its image quality.
And the prior original reader having a lens switchover system provides lenses grouped in one unit, but the lens unit is movable in only one direction, such as a rectangular direction, of the optical axis for changing the lenses. On the other hand, as shown FIG. 18(b), lenses of which the focus length are different are inserted at different positions on optical axis. Additionally, lenses which are not used are evacuated so as not to obstruct the optical angle of the lens being used. Therefore, there is a problem in that the lens unit needs a large amount of space, results in a greater device size. Further because the lens unit provides only a moving means for changing the lens, a high resolution lens of depth of field and depth of focus are sensible to environmental conditions like floating of the manuscript and temperature.
Also in the case of the zoom lens system, it is a very high cost to prepare lenses which have high resolution and few aberrations.
An object of the present invention is to realize original reader including a wide range of resolution, low cost, high accuracy, and compact size.
The present invention comprises the following items as components thereof.
(1) An original reader providing an optical source for lighting the manuscript, a lens focusing an image from the manuscript image, a solid-state image sensor substrate placed on one image projected plane; the original reader further comprises a lens unit including a plurality of lenses corresponding to plural resolution, and a means for moving a lens corresponding to an indicated resolution on the optical axis.
(2) An original reader according to item (1) further comprises a means for moving the lens unit and the solid-state sensor substrate in a direction along the optical axis independently.
(3) An original reader according to item (2) in which the lens unit and the solid-state image sensor substrate are provided in a unit.
(4) An original reader according to item (3) in which the plurality of lenses of the lens unit are arranged in a direction rectangular the optical axis and optical axis and optical axis thereof are parallel to the optical axis.
(5) An original reader according to item (4) in which the optical axes of the plural lenses in the lens unit are each parallel to the optical axis and each lens is set so that optical angle of each lens is not narrowed by an adjacent lens tube.
(6) An original reader according to item (4) or (5) in which the lens unit comprises a frame having plural V grooves of cross section for mounting each lens tube.
(7) An original reader according to item (2) in which the lens unit and the solid-state image sensor substrate are attached to a guide shaft parallel to optical axis.
(8) An original reader of item (7) comprises a means for arranging an angle of the solid-state image sensor substrate to the optical axis.
(9) An original reader according to the item (8) in which the means for arranging the angle of the solid-state image sensor substrate to the optical axis includes means inclining and fixing the solid-state image sensor substrate on a guide shaft having the lens unit.
(10) An original reader according to item (9) comprises a first moving control means for moving the optical unit in a direction parallel to the optical axis, and a second moving control means for moving the optical unit in direction rectangular to the optical axis, and a third moving control means for moving the solid-state image sensor substrate in a direction parallel to the optical axis, and each of the first control means, the second control means, and the third control means are implemented by motor and rack and pinion system.
(11) An original reader according to item (10) in which each of the optical unit, the lens unit and the solid-state image sensor substrate includes means for the vibration suppressing means.
(12) An original reader according to item (11) in which the vibration suppressing means is a pressing matter to press elastically the guide shaft or guide rail.
(13) An original reader according to item (12) in which the pressing matter is formed in one body with the frame.
(14) An original reader according to item (1) in which the optical source and the solid-state image sensor substrate are set within a reading unit, and the optical path in the reading unit is shut from a manuscript.
(15) An original reader according to item (1) comprises a manuscript reading control part, and the manuscript reading control part comprises resolution directing means for indicating the resolution by block unit in a direction to sub scanning over manuscript reading range, and resolution switchover method for changing resolution indicated at block border during manuscript reading action.
(16) An original reader according to item (15) in which the resolution changing control means of the manuscript reading control part moves a corresponding lens in the lens unit along the optical axis according to the specified resolution of the next block when the sub-scan unit reaches a boundary of the block on the manuscript reading range and controls the lens unit and the solid-state sensor substrate to the best position in a direction parallel to the optical axis.